Parking at the airport can easily run $20 per day. That’s in the “cheap” long-term lot, requiring a long shuttle ride to the terminal. Valet service can cost way more. But what if you could get airport parking valet service totally for free—with a car wash and free gas to boot?

That’s the gist of the offer from a startup called FlightCar, which began offering its service at San Francisco International Airport in early February. What’s the catch? In exchange for free parking, a free car wash, and a gas card worth up to $10 for each day the car is left behind, owners agree to allow FlightCar to rent out their vehicles to customers — i.e., strangers. The business model basically brings peer-to-peer car rental services such as Getaround and RelayRides to the airport.

And if you think about it, the airport is the perfect place for a rental handoff. Sign up with FlightCar, and a valet meets you at the airport. That saves drivers the trouble of having to park in the long-term lot and hop on the shuttle to the gate. When a car owner is on a trip, he’s obviously not using the vehicle, so it’s OK that he won’t have wheels for the agreed-upon time. What’s more, a vehicle becomes a money-loser, to the tune of $10, $15, perhaps even $35 per day, when it’s sitting idle parked at the airport.

Those daily fees disappear, however, when the owner agrees to work with FlightCar. Complimentary car washes are thrown into the deal—before and after the car is loaned out—and owners receive gas cards worth $10 for each day the vehicle is rented. FlightCar says it pre-screens all customers and insures vehicles up to $1 million. Wired notes that the company eases the minds of car owners in a few other ways as well:

FlightCar also foots the bill if anything less dramatic goes wrong during the rental, including refilling your tank if the renter doesn’t, compensating you 35 cents per mile if a renter drives over the 90 mile per day limit, and reimbursing you if a renter gets a red-light camera ticket while driving your car.

“When you look at the top 30 airports in the U.S., at any given time there are over 360,000 cars sitting in those parking lots everyday,” Rajul Zaparde, FlightCar’s CEO and one of its co-founders, said, according to betakit. “When you couple that with 120,000 airport car rentals per day, and over $11.3 billion spent per year in car rentals at those 30 airports, you can quickly realize there are huge inefficiencies in the marketplace.”

Why would a renter choose FlightCar over a standard operation like Hertz or Enterprise? For the same reason that consumers could be tempted to skip the standard rental car agency in favor of a peer-to-peer outfit like RelayRides: The prices are cheaper. FlightCar rental rates start at $15 per day, likely saving renters somewhere in the neighborhood of 30% to 50% compared to standard rates.

So far, FlightCar is available only at San Francisco’s SFO airport, but expansion plans are in the works for Orlando, Los Angeles, Phoenix, and Miami—and surely more gateways to come if the service really takes off.